A series of experiments designed to provide information concerning the molecular basis for the interaction of ultrasound with phospholipid model membranes are proposed. These experiments will characterize the effects of chemical and structural variations of the phospholipid membrane and its chemical environment on the acoustic absorption in pure phospholipid vesicles. The variations of absorption with ionic environment, temperature, vesicle size, and phospholipid structure will be correlated with appropriate thermodynamic measurements in an attempt to identify the processes responsible for acoustic absorption in the frequency range from 0.3 to 300 MHz and to elucidate the kinetics of these processes. This study provides the basis for an understanding of the mechanism of interaction between ultrasound and more complicated synthetic and natural membranes, with such an understanding being useful in the guidance and interpretation of research in the diagnostic and therapeutic applications of ultrasound.